<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8">
        <title></title>
        <style type="text/css">

            .parent{
                width: 700px;
                /* height: 500px; */
                margin: 0 auto;
                background-color: antiquewhite;
            }
            .child{
                width: 200px;
                height: 200px;
                display: inline-block;
                background-color: skyblue;
                float: left;
            }
            .clear::after{
                display: block;
                content: "";
                clear: both;
            }
        
        </style>
    </head>
    <body>
        <div class="parent clear">
            <div class="child"></div>
            <div class="child"></div>
            <div class="child"></div>
        </div>
        <div>helloworld</div>
    </body>
</html>